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1. Carbodiimide Ring-Opening Metathesis Polymerization

   https://doi.org/10.1021/acscentsci.3c00032  

   Johnson, J. Drake; Kaplan, Samuel W.; Toth, Jozsef; Wang, Zian; Maw, Mitchell; Sheiko, Sergei S.; Zhukhovitskiy, Aleksandr V. (May 2023, ACS Central Science)
2. Photo-liberated amines for N -carboxyanhydride (PLANCA) ring-opening polymerization

   https://doi.org/10.1039/d1py00781e  

   Goodrich, Sofia L.; Hill, Megan R.; Olson, Rebecca A.; Sumerlin, Brent S. (July 2021, Polymer Chemistry)

   The polymerization of N -carboxyanhydrides (NCAs) affords access to a vast array of synthetic polypeptides with tunable molecular weights, functionalities, and architectures. The use of light to achieve spatiotemporal control over these polymerizations could expand their applicability to a variety of areas, including 3D printing and photolithography. In this report we utilized 2-(2-nitrophenyl)propyloxycarbonyl (NPPOC) as a photoprotecting group to cage a primary amine initiator that is activated upon UV irradiation. NPPOC photocages underwent quantitative deprotection and afforded better polymerization control compared to previously reported photocaged amines for NCA polymerizations. Furthermore, the addition of a small equivalence of base enhanced the control and resulted in polymers with lower dispersities. Overall, this method advances photo-controlled polypeptide synthesis by demonstrating high chain-end fidelity, efficient chain extension, and the ability to synthesize block copolymers. 

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3. Functionalized Polyesters via Stereoselective Electrochemical Ring-Opening Polymerization of O -Carboxyanhydrides

   https://doi.org/10.1021/acsmacrolett.0c00364  

   Zhong, Yongliang; Feng, Quanyou; Wang, Xiaoqian; Chen, Jia; Cai, Wenjun; Tong, Rong (August 2020, ACS Macro Letters)

   null (Ed.)
4. Stereoregular functionalized polysaccharides via cationic ring-opening polymerization of biomass-derived levoglucosan

   https://doi.org/10.1039/D2SC00146B  

   Porwal, Mayuri K.; Reddi, Yernaidu; Saxon, Derek J.; Cramer, Christopher J.; Ellison, Christopher J.; Reineke, Theresa M. (April 2022, Chemical Science)

   We report the facile synthesis and characterization of 1,6-α linked functional stereoregular polysaccharides from biomass-derived levoglucosan via cationic ring-opening polymerization (cROP). Levoglucosan is a bicyclic acetal with rich hydroxyl functionality, which can be synthetically modified to install a variety of pendant groups for tailored properties. We have employed biocompatible and recyclable metal triflate catalysts – scandium and bismuth triflate – for green cROP of levoglucosan derivatives, even at very low catalyst loadings of 0.5 mol%. Combined experimental and computational studies provided key kinetic, thermodynamic, and mechanistic insights into the cROP of these derivatives with metal triflates. Computational studies reveal that ring-opening of levoglucosan derivatives is preferred at the 1,6 anhydro linkage and cROP proceeds in a regio- and stereo-specific manner to form 1,6-α glycosidic linkages. DFT calculations also show that biocompatible metal triflates efficiently coordinate with levoglucosan derivatives as compared to the highly toxic PF 5 used previously. Post-polymerization modification of levoglucosan-based polysaccharides is readily performed via UV-initiated thiol–ene click reactions. The reported levoglucosan based polymers exhibit good thermal stability ( T d > 250 °C) and a wide glass transition temperature ( T g ) window (<−150 °C to 32 °C) that is accessible with thioglycerol and lauryl mercaptan pendant groups. This work demonstrates the utility of levoglucosan as a renewably-derived scaffold, enabling facile access to tailored polysaccharides that could be important in many applications ranging from sustainable materials to biologically active polymers. 

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5. Radical ring-opening polymerization of sustainably-derived thionoisochromanone

   https://doi.org/10.1039/D2SC06040J  

   Prebihalo, Emily A.; Luke, Anna M.; Reddi, Yernaidu; LaSalle, Christopher J.; Shah, Vijay M.; Cramer, Christopher J.; Reineke, Theresa M. (May 2023, Chemical Science)

   We present the synthesis, characterization and radical ring-opening polymerization (rROP) capabilities of thionoisochromanone (TIC), a fungi-derivable thionolactone. TIC is the first reported six-membered thionolactone to readily homopolymerize under free radical conditions without the presence of a dormant comonomer or repeated initiation. Even more, the resulting polymer is fully degradable under mild, basic conditions. Computations providing molecular-level insights into the mechanistic and energetic details of polymerization identified a unique S , S , O -orthoester intermediate that leads to a sustained chain-end. This sustained chain-end allowed for the synthesis of a block copolymer of TIC and styrene under entirely free radical conditions without explicit radical control methods such as reversible addition–fragmentation chain transfer polymerization (RAFT). We also report the statistical copolymerization of ring-retained TIC and styrene, confirmed by elemental analysis and energy-dispersive X-ray spectroscopy (EDX). Computations into the energetic details of copolymerization indicate kinetic drivers for ring-retaining behavior. This work provides the first example of a sustainable feedstock for rROP and provides the field with the first six-membered monomer susceptible to rROP, expanding the monomer scope to aid our fundamental understanding of thionolactone rROP behavior. 

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